1. Field of the Invention
This invention relates to a structure for ultrasonic arrays such as those used in transducers for medical imaging, and in particular to the electrical interconnections of the array elements.
2. Description of the Related Art
In the area of medical imaging, there are the standing goals of making the transducers ever smaller, and of designing transducers that have greater resolution and flexibility, such as the ability to change the aperture. In order to achieve both goals, one must be able to form ever more transducer elements within a given space. The problem then arises that it is also necessary to electrically connect each element to the driving circuitry and, in many cases, to one another. These interconnections also take up space, and also limit how small a transducer element can be.
Interconnection problems are particularly troublesome in multi-dimensional arrays, which are often used to provide variable apertures or focus. For example, in an array that is three elements wide and 128 elements long, in each group of three elements, one element will be between the other two, so that an electrical conductor must be arranged so that it leads to the "middle" element without interfering with the two adjacent outer elements. Providing the necessary interconnects in such arrays often requires complicated, sensitive, and expensive fabrication procedures.
The following references all describe known array structures and fabrication techniques that attempt to address these problems:
1) "Two-Dimensional Array Transducers Using Thick Film Connection Technology," Stephen W. Smith, IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control, Vol. 40, No. 6, pp. 727-34, November 1993; PA1 2) "Fabrication and Characterization of Transducer Elements in Two-Dimensional Arrays for Medical Ultrasonic Imaging," Daniel H. Turnbull and F. Stuart Foster, IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control, Vol. 39, No. 4, pp. 464-75, July 1992; and PA1 3) European Patent Application 0 212 737 (Inventor: 't Hoen, 4 March 1987).
What is needed is an array structure that makes possible either smaller elements in a multi-dimensional ultrasonic transducer array, a more easily fabricated array, or both, with an efficient and easily implemented interconnection arrangement.